The present invention relates to apparatus for converting the energy of surface waves in a liquid, such as an ocean, to more useful forms of energy. Most known systems for harnessing the energy from waves comprise floating structures which are set in motion by the movement of the liquid surface. These systems generally display alternating motions in response to the wave action. Since mechanical energy is more easily used and transferred if in the form of a continuous rotation, sophisticated mechanisms, such as hydraulic pumps and hydraulic motors, have to be used to transform the alternating motions of the various parts into a rotary motion.
One attempt for solving this technical problem has been described in U.S. Pat. Nos. 3,818,703 and 3,818,704. These patents are concerned with a device, having a response to progressive waves in the form of a rotary motion instead of alternated movements. A helically shaped buoyant mass is curved around an imaginary or real axis of rotation. As wave motion progresses along the axis of the helix, the buoyant forces acting on successive sections of the helix impart rotation to the buoyant mass. An energy conversion means, such as a generator, is linked to the rotating helical mass, and may be used to convert the rotational motion to another form of energy.
The above-named patents disclose a generally suitable approach to conversion and use of the energy found in waves within a body of water. However, the apparatus disclosed in these patents suffers from certain serious drawbacks.
Hydrostatics calculations and experiments show that a homogenous simple helix freely floating in still water will not float with its axis horizontal. Its positions of hydrostatic equilibrium are found with the axis tilted with respect to the surface of the water. As the helix is rotated in the water, the angle between the axis and the surface changes. If the simple helix is allowed to float freely and assume one of its positions of stable equilibrium having its axis tilted with respect to the surface of the water, it will be necessary to apply a substantial torque to the helix to move it rotationally from its equilibrium position. Smaller waves will not be effective to provide sufficient torque to set the helix into rotary motion. In waves high enough to overcome the torques resisting motion of the helix, a very irregular rotary motion will occur, along with an alternating tilting motion of the axis.
The only way to alleviate these problems associated with the prior art apparatus would be to maintain the axis of the helix in a horizontal position at the water level. This could be accomplished by fixing the axis in bearings anchored to the marine bed by means of rigid structures or taut mooring cables. This would restore neutral rotational balance. However, as the helix rotates, the center of buoyancy of the helix continually shifts back and forth along the axis thereof while the center of gravity of the helix remains in a fixed axial location. The result would be a cyclically varying stress applied to the bearings supporting the helical mass for rotation. This stress would cause undue wear on the bearings, and increase the expense of constructing and maintaining the apparatus. Also, the need for mooring structures would greatly increase the cost of the apparatus.